Different wave power converters have been developed having individual buoys which by means of their elevation during wave movements transfer power to a generator, a hydraulic pump system or another mechanical energy converter. Wave power converters with accompanying control system form a unit which is arranged in sea areas having as even waves as possible.
Such wave power converters have the advantage over raft systems that they are easier to make storm resistant. Still, such buoyant bodies with accompanying parts are vulnerable to breakdown during storms. This has lead to increased dimensions of mechanical elements with accompanying high costs. In reality it has not yet been possible to build wave power plants with acceptable lifetime and acceptable energy costs based on such wave power converter, due to the need for large dimensions in order to withstand extreme weather, which only is present during a few percentage of the normal operating time.
In addition it is difficult to achieve an optimal buoyant level for the buoyant bodies during operation, mainly due to wave influences, but also due to other water currents and wind. This has also negatively influenced the operating economy.
In Norwegian patent No. 321 085 (Ocean Energy) is described the use of ballast tanks to immerse rafts of buoyant bodies during storm. This has not provided a sufficient storm protection, mainly due to the costs and inconvenience in use.
From U.S. Pat. No. 4,742,241 (Melvin) it is known to pull a raft with wave converters by means of winches. Neither this publication has made a basis for constructing a sufficient wave power plant.
U.S. Pat. No. 7,683,500 describes a device and a method for wave energy conversion. In one embodiment of the device a buoy, a shaft and an electric generator is described. The shaft is connected to the buoy in such a manner that when the buoy moves vertically in response to a passing wave, the shaft is rotated. The shaft is connected to the generator such that the shaft rotation generates electric power. A solution like this has large disadvantages, a.o. it is costly to implement, it requires a substantial and costly maintenance and the lifetime will be rather limited due to the lifetime of the shaft and bearings, which is a well known problem in relation with maritime environments and therefore seeks to be avoided to the extent possible. From WO 2009056854 is known a device for wave conversion based on vertical movement of a buoy. Vertical movement of the buoy is controlled by letting water in through an upper surface of the buoy. The upper surface of the buoy is used to generate hydrodynamic forces that act downwards against upwardly directed forces on a lower surface of the buoy and thereby effectively dampen its movement in case of the presence of a wave which would normally cause undesired large vertical movements of the buoy. The Movement of water on the upper surface can be controlled by adjusting the depth of the float.
Both U.S. Pat. No. 7,683,500 and WO 2009056854 teach that the buoy can be immersed under the sea surface during storm or the like, but they fail in that they can take in water as ballast but cannot get rid of the water and will therefore remain under water if they take in enough water to remove its buoyancy.
In recent years other types of devices for conversion of wave power to be arranged on the seafloor have been developed. Linear generators, hydraulic pumps and recently NASA a.o. have launched a piezo-electric “tension-wire” that can produce energy directly when tensioned.
These are smart solutions in the sense that they avoid the tough weather conditions at the surface and most of these are patented in different variants. Nothing is done, however, with respect to the buoyant body that shall float on the surface, in relation to the extreme weather conditions they may be subjected to. As mentioned above it is described, a.o. in U.S. Pat. No. 7,683,500 and WO 2009056854, that the buoy may be immersed in the water during storm, but as mentioned these are burdened with disadvantages and are not provided with any automatic solution to handle this.
Furthermore none of the known solutions has automatic adjustment means for tide (ebb and flow), currents and constant changes in the wave pattern at the surface for optimal and economically defensible operation of such plants over time.
Furthermore, all the known solutions describe use of rotary movement to recover energy from a buoy which exhibits a mainly linear movement in a vertical direction. As mentioned above the utilization of rotary movement will involve significant use of bearings which will reduce the lifetime and which will increase the installation costs and maintenance costs.
Common features for the known technologies are that they do not satisfy the requirements to production cost, operation, lifetime, degree of efficiency and probability of survival and that they therefore do not offer an economically defensible solution.
In addition the known solutions include a winch arranged at the seafloor which is unfavorable since it is a moist environment, larger reels are required to handle the wire, there are strict requirements to the encapsulation due to the high pressure and there are strict requirements to the bearings due to the moist environment, etc.